This invention generally relates to a process for the aqueous extraction, fractionation and enzymatic treatment of oilseed materials to generate valued products with no significant low value by-product or waste streams. In particular, the fractionation scheme generates a protein-fibre feed ingredient principally for use with ruminant animals and a second dephytinized high protein fraction. The dephytinized high protein fraction has value as feed ingredient for a variety of species of animals.
Considerable efforts have been directed toward developing aqueous processing systems and techniques for the production of high valued protein concentrates and protein isolates ( greater than 90% protein) from oilseeds such as soybean. The objective of all of these existing processing systems and techniques is to generate a single very high valued protein product. Little or no consideration is given to the value of the non-protein component of the starting material. Processing systems have not been devised to fractionate the starting material into a series of valued products without generation of low-valued by-product or waste streams.
Techniques and processing systems targeted toward production of a single high valued protein product from oilseeds often make use of high levels of water and chemicals such as salts, acid or base to achieve efficient protein extraction and isolation. Systems requiring extensive use of water and chemicals are often costly. Further costs are associated with disposing of low-value by-products or waste streams.
Canola or rapeseed consists of approximately 40% oil and 60% non-oil constituents. In commercial processing, most of the oil is removed from the seed either by solvent extraction or by expelling. In processing systems based on solvent extraction, the non-oil material initially exists as a solvent laden white flake or marc. Typically, solvent is removed from the white flake by a process that involves application of steam and heat to generate a final desolventized-toasted product called meal. The meal contains about 35% protein and is sold as a feed ingredient for inclusion in diets feed to a variety of classes of animals including swine, poultry and cattle.
Canola seed protein has excellent feeding value. The protein is rich in methionine (2.0% of total protein) and lysine (5.8% of total protein) with good balance of essential amino acids. In reviewing the nutritional quality of various protein sources, Friedman M. (J. Agric. Food Chem. 44:6-29, 1996) reported a protein efficiency ratio (PER) of 3.29 for rapeseed protein concentrate, 3.13 for casein and 1.60 for soy concentrate. Rapeseed protein concentrate had the highest PER of all of vegetable protein sources reported. As such canola or rapeseed protein, in itself, has excellent feeding value, and can be considered as exceptional in comparison to other plant proteins. Prendergast, A. F., et al. (Nort. Aquacult. 10:15-20, 1994) found that dephytinized rapeseed protein concentrate could replace 100% of the high quality fishmeal in diets feed to rainbow trout without adversely affecting growth performance and feed efficiency of the fish.
Animals do not fully utilize the protein feeding value of canola or rapeseed protein when the protein is supplied in the conventional form as part of the meal. Non-dehulled desolventized-toasted canola meal contains high levels of fibre. Fibre has little feeding for animals such as fish, chickens and young pigs and thus dilutes the protein and energy content of the meal. Further, antinutritional factors, such as phenolics, associated with the fibre may have a negative impact on the performance of monogastric animals such as pigs, chickens and fish. The toasting process employed during preparation of the final meal product decreases the protein solubility of the meal and has been shown to decrease lysine digestibility when fed to chickens (Newkirk, R. W., et al. Poult.Sci. 79:64, 2000). Canola meal contains exceptionally high levels of phytic acid (approximately 3% of the meal). Phytic acid is the storage form of phosphorus in the seed and is poorly digested by monogastric species such as pigs, chickens and fish. Phytic acid can form complexes with minerals, amino acids and proteins and thereby decrease nutrient digestibility. Further, the phosphorus in the phytic acid molecule is largely unavailable to the animal and voided with the faeces. Given this poor digestibility of phytate-P, diets must be formulated with sufficient available dietary P to meet the requirements of the animal and this often increases the cost of the ration. In addition, undigested P in the manure can be damaging to the environment and is of considerable concern in areas of intensive livestock production. Overall, the high fibre and high phytate content of canola meal limits the feeding value as a protein source for monogastric animals such as pigs, chickens and fish.
Ruminant animals, such as cattle, can extract energy from fibre through fermentation in the rumen. Further, rumen microbes can efficiently hydrolyse phytate and thus the potential for antinutritional effects and damage to the environment from dietary phytic acid is less of a concern in feeding ruminant animals. Highly soluble protein is rapidly hydrolysed and utilized by microbes in the rumen. Protein that is resistant to degradation in the rumen but is largely digested during subsequent passage through the small intestine has the highest protein feeding value for ruminant animals. As feed ingredients for ruminant animals, the highly soluble proteins in canola seed are of lower feeding value than the fraction of total canola proteins that are relatively insoluble.
Prior art in this area is focused on methods to achieve efficient protein extraction from oilseed based starting material followed by concentration or isolation of the protein into a single high valued product.
U.S. Pat. No. 5,658,714 teaches that protein can be efficiently extracted from vegetable flour by adjusting the pH of the extract media in the range from 7.0-10.0. Protein is then concentrated by ultrafiltration and precipitated by adjusting the pH of the permeate to 3.5-6.0. The phytate is resistant to the protein precipitation step and thus the phytate content of the final protein concentrate is described as less than 1% of the dry matter in the protein isolate.
U.S. Pat. No. 4,420,425 describes a process of aqueous extraction of defatted soybean using alkaline conditions with an extraction media:oilseed starting material ratio of  greater than 10:1. In this process, solids in the extract are removed by filtration, the solubilized protein is pasteurised, and the extract is passed through an ultrafiltration membrane with a molecular weight cut-off of  greater than 100,000 to generate a protein concentrate.
U.S. Pat. No. 5,989,600 teaches that the solubility of vegetable proteins can be increased by treating the vegetable protein source with enzymes such as phytase and/or proteolytic enzymes. The enzymes are directly applied to the starting material prior to any extraction phase with the objective of improving protein solubility.
U.S. Pat. No. 3,966,971 teaches that acid phytase can be added to an aqueous dispersion of vegetable protein source material to facilitate protein extraction. The aqueous slurry is maintain at a pH of minimum protein solubility for the given protein and subjected to digestion with acid phytase to promote protein solubility. The mixture is heat treated at sufficient temperature to inactivate enzyme activity and solubles are then separated from the insoluble digestion residue. Solubilized residue is described as separated from insoluble residue by centrifugation or filtration or a combination of these procedures. The pH of the liquid extract is then adjusted as desired and dried to generate a final product.
U.S. Pat. No. 4,435,319 teaches that protein can be extracted from sunflower meal by treating an aqueous slurry of the meal with an acid at a pH between 4.0 and 7.0. The soluble and insoluble residues are separated and the insoluble material in continually treated with an acid solution until the desired extraction of protein has been attained. The extracted proteins are then recovered by precipitation or by ultrafiltration.
U.S. Pat. No. 3,635,726 describes a procedure for the production of a soy protein isolate by extraction of the soy starting material under alkaline conditions whereby the pH is above the isoelectric pH of glycinin. After separating the extract from the insoluble residue the pH of the extract is reduced to the isoelectric pH of glycinin to induce protein precipitation.
U.S. Pat. No. 4,418,013 describes a process for the extraction of protein from vegetable protein sources that consists of extraction in water without the use of chemical additives in the water extraction media. The soluble extract is then separated from the solids and diluted into a body of chilled water to induce the formation of protein particles that are then removed from the water and dried to form a protein isolate of that is described as substantially undenatured.
International Patent Publication WO 95/27406 teaches that phytase can be added to water suspension of a soy-based starting material. Under controlled conditions of pH and temperature the phytate content is reduced to  less than 50% of the phytate content in the starting material. In a preferred embodiment of this invention the starting soy material has been exposed to low heat treatment and has a nitrogen solubility index of  greater than 50%. The pH of the effluent is in the range of 7-9 and the effluent is separated into a soluble and insoluble fraction. The soluble fraction is then heat-treated to inactivate enzymes and the solubles are concentrated by nanofiltration and dried to form a final product. The insoluble fraction and the permeate formed during nanofiltration are discarded.
Tzeng et al. (Journal of Food Science 1990. 55:1147-1156) describe a series of experiments on the fractionation of various oilseed materials using an aqueous processing scheme. Commercial canola meal and oil-extracted desolventized non-toasted canola white flake were used as starting materials. All extractions were carried out under aqueous alkaline conditions of pH equal to or greater than 10. In this process, the non-extracted solids residue was separated, and the pH of the extract was adjust to 3.5 to induce isoelectric protein precipitation. The precipitated protein was separated from remaining solubles by centrifugation. The soluble protein was concentrated by ultrafiltration and diafiltration using a 10,000 molecular weight cut-off membrane. The insoluble residue, isoelectric precipitated protein and the ultrafiltered soluble protein were assayed for dry matter, protein, phytate and glucosinolate levels. Under these conditions the non-extracted residue from canola meal contained 67% of the solid and 62% of the protein present in the starting material. On a dry matter basis, the meal residue had a 42% protein and a 5.7% phytate content; the isoelectric precipitate protein had an 83% protein and a 2% phytate content; and the soluble protein had an 86% protein and a 1.7% phytate content. The isoelectric and soluble protein contained 22% and 11% respectively of the total protein in the canola meal starting material. In comparison, protein extraction under alkaline conditions was substantially higher when desolventized non-toasted canola white flake was used as a starting material. In this case, the non-extracted residue contained 50% of the solid and 15% of the protein found in the starting material. On a dry matter basis, the meal residue had an 11% protein and a 6.5% phytate content; the isoelectric precipitate protein had an 87% protein and a 1% phytate content, and the soluble protein had a 96% protein and a 1.2% phytate content. The isoelectric and soluble protein contained 43% and 33% respectively of the total protein in the canola white flake starting material. The very high nitrogen extraction from canola white flake reflects the high nitrogen solubility of the starting material in combination with alkaline extraction conditions.